An electric incandescent ignitor, such as a glow plug, is commonly used in internal combustion engines to assist with cold starting diesel-cycle engines. Diesel cycle engines are designed so that, after the engine warms up, the conditions within the engine combustion chamber are suitable for auto-igniting the diesel fuel and the glow plug is no longer required to assist with fuel ignition.
To reduce engine emissions, fuels that burn cleaner than diesel fuel are being studied. For example, gaseous fuels such as methane, natural gas, propane, and hydrogen can all be burned in an internal combustion engine operating on the diesel cycle to produce lower emissions of oxides of nitrogen (NOx) and particulate matter (PM), compared to an equivalent engine fueled with conventional diesel fuel. Other advantages of injecting such gaseous fuels directly into the combustion chamber of an engine operating on the diesel cycle are that the efficiency and power characteristics associated with the diesel cycle are maintained.
However, such gaseous fuels do not auto-ignite as readily as diesel fuel. Consequently, to convert a conventional diesel engine to operate using a gaseous fuel, a means for assisting ignition is normally required. One strategy for igniting such gaseous fuels is to employ a device for assisting ignition. For example, U.S. Pat. No. 6,076,493, entitled “Glow Plug Shield with Thermal Barrier Coating and Ignition Catalyst”, discloses an apparatus for using a glow plug and shield arrangement for assisting ignition of a fuel with a higher auto-ignition temperature compared to diesel fuel. The '493 patent relates to a combination of a glow plug and a shield having a coating of a thermal barrier material. The '493 patent discloses the desirability of using a catalyst but does not disclose any particular fuel or any particular catalyst formulation, and to the applicants' knowledge, commercialization of such an ignition assist strategy for gaseous fuels has not yet been achieved.
While there are many elements that are known to act as a catalyst not all catalysts perform as well for assisting with ignition of gaseous fuels and there is a need for a catalyst formulation that has the durability required for use in an engine combustion chamber. In addition to pure catalytic compositions comprising one catalytic element, catalytic alloys can also be used, comprising more than one catalytic element, or a catalytic element combined with another material. One catalyst formulation may be effective for one fuel but not as effective for another.
Nevertheless, for an ignition assist apparatus that is employed continuously during engine operation, it remains desirable to provide a catalyst to assist with ignition of the fuel so that the glow plug can be operated at a lower temperature. Lower glow plug operating temperatures are generally associated with longer glow plug service life. Use of a catalyst can also provide an additional element of control over the combustion process. Accordingly, for a gaseous fuel with a higher auto-ignition temperature compared to diesel fuel, there is a need to find preferred catalyst formulations for commercial use in the combustion chamber of an internal combustion engine.
The manufacturing means by which a catalyst is deposited on a glow plug or sleeve disposed around the glow plug can also influence the effectiveness of the catalyst. Accordingly, there is also a need to determine a preferred means for depositing catalyst on a glow plug sleeve.